This invention is generally in the field of gas turbine engines. More particularly, the present invention is directed to a composite blade for a turbine rotor.
Turbine blades are typically manufactured from a casting process in which a molten alloy is poured into a ceramic mold, heated, and then cooled. When the mold is broken off, the blade is then machined to its final shape. This results in a turbine blade having a substantially uniform composition from the root of the blade to the tip. Thus, the alloy chosen for the turbine blade must have suitable performance properties for the thermal and mechanical stresses encountered at various locations on the blade. Such a manufacturing process may not generally allow for a designer to independently select an optimal alloy for different portions of the turbine blade.
In general, the turbine blade is cast from a creep resistant superalloy. In an exemplary turbine blade casting process, the superalloy is directionally solidified from root tip. During operation, turbine blades tips are exposed to extreme temperatures and stresses which cause them to oxidize and crack. A turbine blade may crack along grain boundaries at or near the tip of the airfoil and the crack will propagate along the length of the airfoil. Eventually a blade may suffer enough damage to compromise the turbine's efficiency. A blade is typically replaced before it reaches this level of damage.